The invention relates to an electrical rotary drive in accordance with the preamble of independent claim 1, and to a blood pump with a rotary drive of this kind.
Blood pumps, which are usually designed as axial or as centrifugal pumps, serve for the forwarding of blood and are used for example in the framework of operations on the heart for maintaining the blood circulation. Furthermore, implantable blood pumps are known which are implanted into the body of the patient for the temporary or chronic support of the heart activity.
In blood pumps it must be ensured that no contamination of the forwarded blood occurs. Therefore in blood pumps the rotor of the electromagnetic drive and/or the pump rotor is/are preferably magnetically journalled without contact. This magnetic journalling of the rotor can be realized either through separate magnetic bearings, that is, bearings which are different from the drive; or the magnetic journalling is realized by the stator of the drive.
In WO-A-96/31934 for example a rotation pump is disclosed which is suitable as a blood pump and which is designed as a so-called bearingless motor. This is an electromagnetic rotary drive in which the rotor is journalled without contact with respect to the stator by means of magnetic forces, with no separate magnetic bearings being present for the rotor. For this the stator is designed as a bearing and drive stator comprising a drive winding and a control winding. With these two windings a magnetic rotary field can be produced which on the one hand exerts a torque on the rotor which causes it to rotate, and which on the other hand exerts any desired settable transverse force on the rotor, so that its radial position can be actively controlled or regulated respectively. Thus three degrees of freedom of the rotor can be actively regulated. With respect to three further degrees of freedom, namely its axial deflection in the direction of the axis of rotation and tiltings with respect to the plane which is perpendicular to the axis of rotation (two degrees of freedom) the rotor is passively magnetically, which means not controllably, stabilized through reluctance forces.
The term xe2x80x9cbearingless motorxe2x80x9d is to be understood in this sense for the following explanations. With respect to the further details of the design and especially of the control or regulation respectively of the bearingless motor, reference is made here, in addition to the already cited WO-A-96/31934, to WO-95/18925.
Furthermore, blood pumps should be compact and space saving, in particular in the case of an implantation in the body, but nevertheless be able to achieve a pumping performance which corresponds at least to that of the heart. For this it is proposed e.g. in WO-A-96/31934 to provide the rotor of the bearingless motor with vanes, so that the rotor of the rotary drive is identical to the pump rotor, and thus forms an integral rotor. This rotor thus serves as a drive rotor, a bearing rotor and a pump rotor, through which a very compact and high performance blood pump can be realized.
A problem in known bearingless motors is to be seen in that when faults arise, such as for example the failure of an amplifier stage or the breaking of an electrical line in one of the phases of the stator, a correct functioning of the drive and/or of the magnetic journalling of the rotor is no longer ensured. This represents an enormous safety hazard in particular in very sensitive uses, e.g. in implanted blood pumps. A failure of the rotor drive or of the magnetic rotor journalling can namely have very severe, possibly even fatal consequences. The invention is thus dedicated to the task of significantly reducing this safety hazard.
The object of the invention is therefore to provide an electrical rotary drive which is designed as a bearingless motor and which is fault tolerant both with respect to the magnetic journalling of the rotor and with respect to the driving of the rotor, which means that a correct operation of the bearingless motor with reliable magnetic journalling of the rotor and reliable driving of the rotor should still be possible when faults arise.
The electrical rotary drive which satisfies this object is characterized by the features of the independent claim 1.
The electrical rotary drive in accordance with the invention, designed as a bearingless motor, thus has a magnetically journalled rotor and a stator which comprises a drive winding having at least two loops for producing a magnetic drive field which produces a torque on the rotor, and a control winding having at least three loops for producing a magnetic control field by means of which the position of the rotor with respect to the stator can be regulated, with each loop of the drive winding belonging to a different electrical drive phase, and with each loop of the control winding belonging to a different electrical control phase, as well as a setting device which provides each loop of the drive winding and each loop of the control winding with a phase current or a phase voltage as a setting parameter, with the setting device being designed in such a manner that the setting parameter for each loop of the drive winding and for each loop of the control winding can be regulated independently of the setting parameters for the other loops.
For this the setting device preferably comprises for each loop of the drive winding and for each loop of the control winding a separate bipolar power amplifier, which is integrated into a control apparatus for the rotary drive.
The rotary drive in accordance with the invention, which is designed as a bearingless motor, operates in fault-free normal operation with at least two drive phases and at least three control phases. The terms xe2x80x9cdrive phasexe2x80x9d and xe2x80x9ccontrol phasexe2x80x9d respectively are used in each case to mean a loop of the drive winding or of the control winding respectively and the part of the setting device which supplies it. Since the setting parameters, that is, the phase voltage or the phase current, can be regulated for each loop of the drive winding and for each loop of the control winding completely independently of the setting parameters for the other loops, each drive phase and each control phase can be operated independently of the remaining electrical phases. Thus the rotary drive can continue to be operated with a reduced number of drive phases and/or control phases respectively when a fault arises in a drive phase and/or a control phase, e.g. in the event of a failure of a complete phase, without concessions regarding the correct functioning either of the magnetic journalling or of the driving of the rotor of the rotary drive being necessary.
The minimum requirement for an enduring correct operation is that one drive phase and two control phases of the rotary drive are still fault-free, which means that at least one drive phase and at least one control phase can fail completely without the reliable operation of the rotary drive being endangered. Depending on how many drive and control phases the rotary drive in accordance with the invention is equipped with, it can still continue to be operated even after a failure of a plurality of drive and/or control phases.
Since the rotary drive in accordance with the invention can be operated with a reduced number of phases, it is in principle irrelevant where a fault arises in a drive phase or in a control phase. Thus for example a power amplifier can fail, or a break can occur in a line in one loop of the drive winding or of the control winding respectively, or a short circuit can arise in a power amplifier or in a winding loop of the drive or the control winding; and in spite of such a fault a further reliable operation of the rotary drive is possible. As a result of this high fault tolerance the rotary drive in accordance with the invention brings about a considerable increase in the operating reliability.
The rotary drive in accordance with the invention with its at least two-phase design of the drive winding in the fault-free normal case is preferably a permanent-magnetically excited rotary field motor, thus in particular a permanent-magnetically excited synchronous motor or a brush-less d. c. motor (in spite of its generally usual name, the latter is essentially a rotary field motor). This means that the drive field which is produced by the stator is a rotary magnetic field, which drives the permanent-magnetic rotor. In the event that only one fault-free phase is available any longer for the operation due to a fault in one or more drive phases, then the rotary field motor becomes a single-phase a. c. motor.
The design of the bearingless motor as a permanent-magnetically excited rotary drive, that is, with a permanent-magnetically excited rotor, has the advantage in contrast with field-excited rotary drives that no current and thus no energy is required for the field excitation. The permanent-magnetic excitation thus enables a very economical operation with a comparatively low energy consumption This is a substantial advantage in particular for blood pumps and especially for implantable blood pumps, since in general an arbitrarily large energy supply is not available for the latter.
As is usual for the bearingless motor (see z. B. WO-A-98/11650) those designs of the rotary drive in accordance with the invention are preferred in which the drive winding has a number of pole pairs equal to p and the control winding a number of pole pairs equal to p+1 or pxe2x88x921, which means that the numbers of pole pairs of the windings differ by one.
In accordance with a preferred exemplary embodiment the rotary drive has exactly three drive phases and exactly three control phases. In a design of this kind the rotary drive can still reliably drive and journal the rotor even in the event of the complete failure of two drive phases and one control phase.
In particular in regard to a design which is as compact, simple and space saving as possible, those embodiments are furthermore preferred in which exactly two drive phases and exactly four control phases are provided. Through this measure it is possible to reduce the number of stator teeth and the number of coils for the drive and the control winding, through which the cost and complexity of the apparatus, the complexity and size of the bearingless motor can be reduced. At the same time the fault tolerance with respect to the failure of one drive phase and the failure of at least one control phase is preserved. In embodiments of this kind the stator preferably has exactly eight stator teeth, between which the rotor is journalled. This has the additional advantage that there is more room in the grooves between the stator teeth, for example for sensor elements of the position sensors.
In accordance with a preferred embodiment the control winding comprises a plurality of concentrated control coils, each of which is wound around a different stator tooth.
In regard to a fault tolerance of the bearingless motor in accordance with the invention which is as great as possible, two separate control systems are preferably provided, each of which comprises the following components:
at least two position sensors for measuring the radial position of the rotor in the stator,
means for determining the rotor angle, for example field sensors,
at least three power amplifiers for supplying the individual loops of the drive and the control winding,
a signal processing and regulation device for the regulation of the drive and the position of the rotor and for controlling the power amplifiers,
with each control system controlling at least one drive phase and at least two control phases.
Through this measure the bearingless motor is operated by two nearly identical control systems, which can operate independently of one another. Since each control system comprises the components which are necessary for the operation of the bearingless motor, such as e.g. position sensors, means for determining of the rotor angle and regulation devices and power amplifiers for at least one drive phase and at least two control phases, each control system can take over the control and the regulation of the bearingless motor alone and immediately. In fault-free normal operation both control systems control the bearingless motor in common. In the event of a fault, however, the reliable operation can immediately be ensured with one of the two control systems. This so-called hot redundancy brings about yet a further considerable increase in the fault tolerance and thus in the operating reliability.
Furthermore, communication means are preferably provided for the communication between the two control systems. From this a further increase in the operating reliability results in particular in normal operation, in which both control systems are active. Since for example each control system has its own position sensors, the measurement of the position of the rotor is overdetermined in normal operation. In that the control systems have communication means which exchange the values for the position of the rotor which they in each case measure, this redundancy can advantageously be used for checking the position sensors. Analogous remarks hold for the field sensors and the rotor angle respectively.
Furthermore, fault detection means are preferably provided, by means of which faults in the control systems and/or in the individual drive phases and/or in the individual control phases and/or in the energy supply can be detected. These fault detection means can be designed as components both of the hardware and of the software. In accordance with a further advantageous measure the fault detection means can, in the event of the detection of a fault, eliminate the latter or switch over the rotary drive into a suitable one of a plurality of possible fault modes depending on the nature of the fault. In these fault modes parts of a control system or else an entire control system, or individual loops of the drive or control winding can be deactivated. Since more than one fault mode is provided, the control systems can react very flexibly and in a manner which is adapted to the respectively arising fault and take only the respectively necessary components out of operation, or no longer use them respectively.
In particular in regard to blood pumps it should be possible to design the bearingless motor in accordance with the invention very compactly and space savingly. In this regard it is advantageous to design each control system at least partly in the form of electronic prints which are arranged in the interior of the rotary drive.
In this the electronic prints which are arranged in the interior of the rotary drive are all power amplifiers and are arranged in such a manner that the individual power amplifiers are in each case connected directly to the associated drive and control coils respectively, that is, without cables. Through this measure the number of cable wires which lead away to the outside from the bearingless motor can be reduced to a minimum. Since experience shows cable connections to have the highest dropout rate of all components, a further increase in the reliability results from this.
The arranging of the electronic prints in the interior of the rotary drive is possible without problem in particular in combination with a preferred design of the rotary drive as a so-called temple motor. In a temple motor, such as is for example disclosed in WO-A-98/11650 (See FIG. 8 there and the associated text passages), the stator has a plurality of stator teeth which are connected by a yoke and which are in each case formed in L shape, with the longer limb extending in the axial direction, which is determined by the desired axis of rotation of the rotor, and with the shorter limb extending radially inwardly. Here the electronic prints can be arranged in the space which is surrounded by the longer limbs of the stator teeth.
A further advantageous measure consists in providing an evaluation module for the position sensors in a temple motor which is designed as an electronic print and which is arranged on the shorter limbs of the stator teeth in such a manner that the components which are provided on the electronic print are located in the free space between the stator teeth. An ideal utilization of the space in the bearingless motor results from this.
It is also advantageous to connect individual electronic prints to one another through flexible connection prints (flexprints). The substantially rigid electronic prints and the flexprints thus form namely a compound, a so-called rigid flex compound, which can be manufactured, equipped and tested as a unit.
Furthermore, a blood pump with an electrical rotary drive in accordance with the invention is proposed by the invention, with the rotor of the rotary drive being permanent-magnetically excited and having a plurality of vanes for forwarding the blood, so that the rotor of the rotary drive also serves as pump rotor. A blood pump of this kind is fault tolerant to a high degree, extremely reliable, compact, of high performance and economical in regard to the energy requirement. It is suitable for uses inside and outside the body.
Further advantageous measures and preferred designs of the invention result from the subordinate claims.